1. Field of the Invention
The present invention relates generally to a heat dissipation structure for use in combination with an electronic circuit board. The invention relates further to a method of producing an electronic circuit board assembly including a heat dissipation board.
2. Description of the Prior Art
Heat dissipation boards have been extensively used for electronic circuit boards on which heat generating electronic components are mounted. Japanese Patent Application Publication No. 10-84063, for example, discloses a heat dissipation structure as shown in FIG. 1. As shown therein, a heat dissipation board 33 is in an inversed U-shaped configuration in cross-sectional view with heat dissipation fins 33a formed on the top surface thereof. An electronic circuit board 32 is fixed to the lower face of the heat dissipation board 33 to form a space 33b in which heat generating electronic components 31 are accommodated. Other electronic components 34 are mounted on the reverse side of the electronic circuit board 32.
A molten resin 35 is injected into the space 33b from a resin injection port 33c formed in the side surface of the heat dissipation board 33 to mold the electronic components 1. Air discharge port 33d is formed in the opposing side surface of the heat dissipation board 33 to ease the injection of the molten resin. With this structure, molding the heat generating electronic components with the resin improves heat dissipation efficiency.
The present invention provides a new heat dissipation structure that has excellent heat dissipation capability. The present invention also provides a manufacturing method for manufacturing an electronic circuit board assembly having the heat dissipation structure.
An electronic circuit board assembly according to the present invention includes an electronic circuit board on which a plurality of electronic components are mounted, an electrical insulation sheet, and a heat dissipation board in facial contact with the electronic circuit board with the electrical insulation sheet interposed therebetween. The heat dissipation board is formed with at least one recessed portion on a top surface facing the electronic circuit board and having side surfaces connecting to the top surface. A heat dissipation material, such as a gel-like resin, is coated over the recessed portion and at least one electronic component from the plurality of electronic components is accommodated in the recessed portion over which the heat dissipation material is coated. An amount of the dissipation material is such that the heat dissipation material fills a gap between the electronic component and the side walls and the bottom wall of the recessed portion.
With the electronic circuit board assembly thus constructed, the heat dissipation board dissipates heat through the heat dissipation material and also from a side surface of the electronic component, thereby improving the heat radiability. Moreover, in the case where the electronic component is a semiconductor device, the heat of the high-temperature terminal is radiated through the resin as well as through the wiring pattern on the circuit board and the insulating sheet between the circuit board and the heat dissipation board, whereby the heat in radiated with high efficiency.
For the heat dissipation board formed with a plurality of recessed portions on the top surface thereof, at least two recess portions may have different depths. In this case, the depth of the recessed portion is determined depending on a height of the electronic component to be accommodated.
A through-hole and/or a notch may be formed in the electronic circuit board to allow the heat dissipation material to escape from the recessed portion when the electrical component is intruded into the recessed portion. With the through-hole or notch formed, air bubbles can be prevented from being generated between the electronic circuit board and the recessed portion, thereby being capable of improving the heat radiability
Further, the recessed portion formed in the heat dissipation board may extend to at least one of the side surfaces of the heat dissipation board. In this case, the heat dissipation material is filled over an area covering the one of the side surfaces of the heat dissipation board. By doing so, the electronic component can be mounted in alignment with the side surface of the heat dissipation board, so that a space for accommodating the electronic components is enlarged enough to increase a degree of freedom of mounting the electronic components, thereby attaining a higher density of mounting the electronic component on the printed-circuit board.
According to another aspect of the present invention, there is provided a method of manufacturing an electronic circuit board assembly includes forming a recessed portion in the top surface of the heat dissipation board to extend to at least one of the side surfaces, coating the recessed portion with a gel-like resin having heat dissipation capability, bringing the electronic circuit board into facial contact with the heat dissipation board with the electrical insulation sheet interposed therebetween so that at least one electronic component from the plurality of electronic components mounted on the electronic circuit board is buried in the gel-like resin. The gel-like resin coated in the recessed portion is such an amount that a gap between the electronic component and side surfaces and bottom surface of the recessed portion is filled with the gel-like resin and an excess amount of the gel-like resin is expelled out of the one of the side surfaces of the heat dissipation board. Finally, the gel-like resin protruded from the side surface of the heat dissipation board is removed.
Thus, the gel-like resin is partially made to swell out of the opening of the recessed portion on the side surface of the heat dissipation board by intruding the electronic component into the resin to be removed. Therefore, the electronic component can be intruded in a state where the recessed portion is sufficiently filled with the resin, and the air bubbles is prevented from being generated, thereby being capable of ensuring the thermal conductivity in the resin. Further, the space for accommodating the electronic component is enlarged enough to increase the degree of freedom of mounting the electronic component, thereby attaining a higher density of mounting the electronic components on the printed-circuit board.